The present invention relates generally to electronic ballasts for powering one or more light sources. More particularly, this invention pertains to a universal dimming ballast platform for powering light sources in accordance with a plurality of lighting applications.
Program start dimming ballasts as are known in the art are useful in environments where light sources (e.g., lamps) are frequently turned on and off, and light levels need to be adjusted to save energy. Typically, a dimming ballast can only drive one type of lamp because the filament voltage is specially designed for this type of lamp.
Certain dimming methods as known in the art wherein the filament heating voltage and lamp current are inversely controlled in a directly proportional manner. These conventional methods are less than optimal, in that the heating voltage and lamp current cannot be adjusted independently. The filament heating is set in such a way that when the lamp is at a minimum holding current the filament heating is set at a maximum level, and when the lamp current is modulated to one hundred percent, the filament heating is at a minimum level. Further, where the lamp current is a PWM current controlled between a maximum and a minimum setting the lamp current crest factor will be much greater than 1.7. Lamp life is generally reduced in accordance with high lamp current crest factors greater than 1.7 and therefore this rating is strongly recommended by lamp manufacturers and the industry in general.
It would be desirable to provide, then, an electronic ballast that can drive multiple types of lamps and independently adjust filament heating voltage according to requirements of a particular lamp current.
It would be further desirable for the electronic ballast to provide continuous dimming, and PWM filament heating rather than PWM lamp current control, such that the lamp current envelope is flat and the lamp current crest factor is appropriate.